The amplitude modulated (AM)-vestigial sidebands (VSB) 6 Megahertz (MHz) television (TV) broadcast system only supports one standard definition video channel plus a pair of stereo audio channels and two auxiliary audio channels. In 1995, the Federal Communications Commission (FCC) adopted the Advanced Television System Committee (ATSC) broadcast standards for digital TV (DTV) (e.g., A/53B, A/65B, A/90, etc.). With support of motion picture experts group (MPEG) multiple program transport streams (MPTSs), the ATSC DTV standards include dynamic support for and transport of one or more program streams (e.g., each containing video plus audio) within a single 6 MHz broadcast channel. For example, a broadcaster may simultaneously provide a football game, a local news program, and weather information within a single MPTS. The ATSC DTV standards support an effective payload of approximately 19.3 Megabits per second (Mbps) for a terrestrial 6 MHz broadcast channel or approximately 38 Mbps for a 6 MHz cable broadcast channel.
FIG. 1 is a schematic illustration of an example prior art transmitter 100 for the prior art ATSC DTV broadcast system. A plurality of application encoders 105 principally perform data compression and encoding for a plurality of sources 110 (e.g. video, audio, data, etc.) to reduce the number of bits required to represent the sources 110. For example, the ATSC DTV system uses MPEG-2 compression for video sources and the ATSC compression standard (AC-3) for audio sources. A plurality of outputs 115 (i.e., program streams) of the application encoders 105 are provided to a transport packetizer and multiplexer (TPM) 120 that divides each of the program streams 115 into packets of information (including the addition of uniquely identifying information) and multiplexes the plurality of packetized program streams 115 into a single MPTS 125. The TPM 120 also receives, packetizes, and multiplexes program and system information protocol (PSIP) information 127 into the MPTS 125. Finally, a modulator 130 uses the MPTS 125 to modulate a carrier to create a radio frequency (RF) transmission 135. The modulator 130 uses either 8-VSB or 16-VSB. Example implementations of the application encoders 105, the TPM 120, and the modulator 130 are well known to persons of ordinary skill in the art, and, thus, will not be discussed further.
The PSIP information 127 (as defined in ATSC standard A/65A) is a small collection of hierarchically arranged tables designed to operate within every MPTS to describe the programs carried within the MPTS. There are two main categories of PSIP information 127: system information and program data. System information allows navigation and access of the channels (i.e., program streams) within the MPTS, and program data provides necessary information for efficient selection of programs. Some tables announce future programs, and some are used to logically locate current program streams that make up the MPTS.
FIG. 2 is an example set of PSIP information tables 200 illustrating the relationships between the various tables. The master guide table (MGT) 205 provides indexing information for the other tables. It also defines table sizes necessary for memory allocation during decoding, defines version numbers to identify those tables that are new or need updating, and generates the packet identifiers (PID) that label the tables. For example, MGT 205 entry 207 points to the zeroth (i.e., original) version of a ratings region table (RRT) 210. The RRT 210 is designed to transmit the ratings system in use for each country. For example, in the United States the RRT 210 represents the television parental guidelines (TVPG), more commonly referred to as the “V-chip” system. A system time table (STT) 215 is a small data structure that serves as a reference for time of day functions, e.g., to manage scheduled events, display time-of-day, etc.
A virtual channel table (VCT) 220 contains a list of all the channels that are or will be active, plus their attributes, e.g., channel name and number. Event information tables (EITs) 225a-b describe the program(s) for a time interval of three hours. There may be up to 128 EITs, EIT-0 through EIT-127, allowing for up to 16 days of programming to be advertised in advance.
Example implementations of generating PSIP information, PSIP tables, PSIP packets, and decoding PSIP information and tables are well known to persons of ordinary skill in the art and, in the interest of brevity, will not be discussed further.
FIG. 3 further illustrates information contained in the VCT 220. In the example table, Short Name is typically displayed in the upper corner of a TV screen to identify a channel and Type indicates the type of channel. Major Channel indicates a 6 MHz RF broadcast channel, with Minor Channel indicating sub channels. Source ID provides a PID within a MPTS, and Extended Names are typically displayed in an electronic program guide (EPG). The VCT 220 facilitates selection and location of programs by a receiver or a user of a set-top box or television. The VCT 220 can be updated in real-time so that situations like over-time (OT) in sporting events can be supported in addition to the regularly scheduled programs, reducing the number of times that programs are “joined in progress.”
FIG. 4 illustrates an example portion of a programming line-up transported in a MPTS showing how bandwidth of the MPTS could be utilized to support multiple simultaneous programs. The example of FIG. 4 conveys several points:
1. Bandwidth requirements are dynamic. In the case of nondeterministic programs, like sports, an allocation may change on a moment by moment basis.
2. The number of programming streams will change as programming options change.
3. The UT vs. A&M OT situation underscores the dynamic nature of the MPTS.
4. Services such as Weather Graphics, Text and other low bit rate services may also be supported.
5. Names of channels may change as the programming line up changes.
The PSIP tables provide the necessary information so that an EPG can be created and/or updated, but also so that a receiver can locate, select and display programs. There are several subtle differences that exist between the PSIP protocols for terrestrial broadcast and the cable multiple service operator's PSIP. These slight differences are standardized, well understood by those of ordinary skill in the art, and, will not be discussed further. However, a device supporting both terrestrial and cable broadcasts, must support both forms of PSIP information.